A solid polymer fuel cell is basically composed of a polymer electrolyte membrane which selectively transports hydrogen ion and a pair of catalyst electrodes (fuel electrode and air electrode) which sandwich the polymer electrolyte membrane. The fuel cell which has the above structure can continuously take out electric energy by supplying fuel gas (hydrogen is contained) to the fuel electrode, and supplying oxidizing gas (oxygen is contained) to the air electrode.
The polymer electrolyte membrane is composed of an electrolyte which contains a polymer ion-exchange membrane or the like, such as a sulfonic acid group-containing fluorine resin ion-exchange membrane or hydrocarbon resin ion-exchange membrane. Further, in order for the polymer electrolyte membrane to have an ion transport function, it needs to contain a given quantity of water.
The catalyst electrode is composed of a catalyst layer that is arranged on the polymer electrolyte membrane side and promotes a redox reaction therein and of a gas diffusion layer that is arranged on top of the catalyst layer and has both air permeability and electric conductivity. The catalyst layer is mainly composed of carbon powder carrying a platinum group metal catalyst. A polymer electrolyte membrane integrated with a pair of catalyst electrodes (catalyst layer and gas diffusion layer) is called a membrane electrode assembly (hereinafter also referred to as “MEA”).
Further, a technique is known in which the edge of an MEA is surrounded by a frame with high rigidity in order to facilitate easier handling of an MEA with low rigidity (for example, see Patent Literatures 1 and 2). A member composed of an MEA and a frame surrounding the edge of the MEA is called a frame-integrated MEA.
FIG. 1A is a plan view of frame-integrated MEA 1 disclosed in Patent Literature 1. FIG. 1B is a cross-sectional view of frame-integrated MEA 1 of FIG. 1A, taken along line AA.
As shown in FIG. 1A, frame-integrated MEA 1 includes membrane electrode assembly (MEA) 5 and frame 6 surrounding the edge of MEA 5. Further, as shown in FIG. 1B, MEA 5 is composed of polymer electrolyte membrane 5A and a pair of catalyst electrodes 5D (fuel electrode and air electrode) sandwiching polymer electrolyte membrane 5A. Catalyst electrode 5D is composed of catalyst layer 5B disposed on polymer electrolyte membrane 5A and gas diffusion layer 5C disposed on catalyst layer 5B. Frame 6 is adhered to polymer electrolyte membrane 5A.
Further, a technique is known in which the amount of cracks to be formed in a surface of a catalyst layer is adjusted (for example, see Patent Literature 3).
Further, a technique is known in which a reinforcement member is connected to an MEA by hot pressing so as to cover the edge of a catalyst layer in order to facilitate easier handling of the MEA (for example, see Patent Literatures 4 to 6).